Internal combustion engine lubricating system

A lubricating system of an internal combustion engine comprising:

• an oil relief valve provided with a housing provided with a relief port on the peripheral wall, a plunger provided with a pressure receiving surface at one end, enabling opening or closing of said relief port and fitted to the housing so that the plunger can be reciprocated and spring means for pressing the plunger in a direction in which said relief port is closed;
• said oil relief valve being adapted to be disposed in oil in a cast oil pan connected to the lower end of a crankcase and being positioned at approximately a halfway portion of a feed oil passage connecting an oil pump and an oil filter, wherein the oil filter is attached to the outside surface of the oil pan;
• an oil passage constituting a part of said feed oil passage, said oil passage extends approximately horizontally and connects to the oil filter and a connecting hole which is provided with an axis approximately perpendicular to said oil passage for communicating with approximately a middle part of said oil passage and is open on an upper surface of a passage forming part formed in said passage forming part integrated with a bottom of the oil pan;
• the oil relief valve being supported by at least one of the oil pan and the crankcase is coaxially connected to said connecting hole with the pressure receiving surface of the plunger directed downwardly;
• the oil relief valve is surrounded on the side of an oil strainer arranged in the oil pan and connected to an oil pump;
• and
• a wall rising to a higher position than the position of the relief port of the oil relief valve is integrated with the bottom of the oil pan.